Effect of braking pressure and braking speed on the tribological properties of C/SiC aircraft brake materials Shangwu Fan * , Litong Zhang, Laifei Cheng, Guanglai Tian, Shangjie Yang National Key Laboratory of Thermostructure Composite Materials, P.O. Box 547, Northwestern Polytechnical University, Xi’an, Shaanxi 710072, China article info Article history: Received 4 December 2009 Received in revised form 31 January 2010 Accepted 12 February 2010 Available online 19 February 2010 Keywords: A. Ceramic–matrix composites B. Friction/wear E. Liquid melt infiltration abstract Effects of braking pressure and braking speed on the tribological properties of C/SiC aircraft brake mate- rials has been studied using a disk-on-disk type laboratory scale dynamometer. The braking temperature increased with increasing braking speed and was less affected by changes in braking pressure. The fric- tion coefficient increased to the maximum value at 10 m/s and then fell with the increase of braking speed at the same braking pressure. The friction coefficient decreased with the increase of braking pres- sure at the same braking speed. The wear rate increased with braking speed increasing at the same brak- ing pressure. The wear rate was little at braking speed below 20 m/s, and rapidly increased when the braking speed exceeded 20 m/s. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction C/SiC composites are new type of high performance brake mate- rials developed after powder metallurgy (PM) and C/C composites [1]. The advantages of PM brakes are the maturity in material development and low cost, while the application of PM brakes is limited by their major disadvantages such as high weight, poor performance at high temperature, and prone to corrosion [2,3]. C/C brakes were developed to overcome the disadvantages of the PM brakes, exhibiting excellent thermal and mechanical properties with lower weight. However, the C/C brakes suffer from insuffi- cient stability of friction coefficient caused by humidity [4–6]. Combining the advantages of PM and C/C brakes, and overcoming most of the disadvantages of PM and C/C brakes, C/SiC composites exhibit some other superior performances such as high and stable friction coefficient, long life, low wear rate, and lower sensibility to surroundings and oxidation [3,7–10]. In the early 1990s, Krenkel et al. at the German Aerospace Cen- ter (DLR) in Stuttgart started investigations of C/SiC composites for high performance automobile applications [11]. Up to now, the C/ SiC brakes have been successfully applied to Porsche, Ferrari and Daimler Chrysler [12,13]. Investigations by the Ceramic Composite Aircraft Brake Consortium of USA indicated that C/SiC materials may be feasible as a next-generation aircraft brake material [7]. Nowadays, plenty of work have been done for developing C/SiC air- craft brake materials [7,14–19]. In 2008, the C/SiC aircraft brakes were installed on a certain airplane for trial flight and achieved success which were prepared by Northwestern Polytechnical Uni- versity and Xi’an Aviation Braking Science and Technology Co., Ltd. in China [20]. However, the systematical research for the effects of braking parameters on the tribological properties of C/SiC aircraft brake materials has seldom been reported. In the present paper, effects of braking parameters on the tribological properties of C/SiC air- craft brake materials are systematically investigated. 2. Experiments 2.1. Fabrication The C/SiC aircraft brake materials were fabricated by chemical vapor infiltration combined with liquid melt infiltration (LMI). The C/SiC were composed of 65 wt.% C, 27 wt.% SiC, and 8 wt.% Si. The density and porosity were 2.1 g cm À3 and 4.4%, respectively [18]. 2.2. Testing methods The tribological properties were tested on a disk-on-disk type laboratory scale dynamometer (Fig. 1) by reference to [18]. The ki- netic energy absorbed by braking was supplied by the inertia wheels, which were driven by a DC motor. The tested specimens acted as both rotor and stator. When the inertial wheel, which ro- tated with the rotor specimen simultaneously, was accelerated to a certain rotational velocity, braking was achieved through the fric- tion between the rotor and stator under a certain braking pressure. Rotating velocity, braking moment, and braking time were 0266-3538/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2010.02.012 * Corresponding author. Tel.: +86 29 8849 4622; fax: +86 29 8849 4620. E-mail addresses: fshwu@163.com, shangwu_fan@nwpu.edu.cn (S. Fan). Composites Science and Technology 70 (2010) 959–965 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech